The emphasis on fuel economy has been increased in recent years. One approach to improve the fuel economy of vehicles is to design new lubricant oils that reduce friction and have lower high-temperature high-shear (“HTHS”) viscosity, while maintaining a good film thickness for durability. In an attempt to improve fuel economy and to reduce vehicle CO2 emissions, the use and stipulation of low viscosity grades by the Original Equipment Manufacturer (OEM) is becoming increasingly widespread. In Europe, several OEMs are looking at 0W-xx and 5W-xx viscosity grades for passenger car gasoline and diesel vehicles. For example, Volkswagen (VW) and Bayerische Motoren Werke (BMW) have 0W-20 specifications. The BMW specification is known as LL-14FE+.
One of the challenges for the provision of engine oils having these reduced viscosity grades is maintaining engine cleanliness. Such engine oils must be able to reduce engine sludge and provide good soot handling, and wear protection, whilst providing desired fuel economy benefits. These targets should be achieved while maintaining low levels of sulphated ash and phosphorus, as well as ensuring seal compatibility. Viscosity index improvers (“VII's”) play an important role in formulating engine oils with these desired properties. There is a need to provide new engine oils having low viscosity grades that meet these requirements.
Another challenge for these low viscosity grade engine oils is that some OEM's are requiring or will require that the engine oils pass the OM646LA engine wear test. Thus, in some cases the engine oil formulations must be suitable for passing the several requirements of this test.
With an increase in oil temperature, the viscosity of an engine oil generally decreases and with decreasing oil temperature, the viscosity of the oil generally increases. Modern engines typically operate at high temperatures. It is important to maintain the viscosity of the engine oil within a specified range while the engine is operating at these high temperatures to properly lubricate moving parts of the engine. Additionally, the engine oils may be exposed to low temperatures from the environment when the engine is not running. Under these conditions, the viscosity of the oil must remain low enough so that the oil will flow at the temperatures encountered under engine starting conditions. Acceptable oil viscosity ranges for various temperatures are specified by the SAE J300 standard.
Engine oils also encounter high shear rates when used in engines. Shear rates as high as 106 s−1 have been reported in literature. The viscosity behavior of lubricants under high temperature high shear (HTHS) conditions may have an impact on fuel economy. Fluids with relatively high HTHS viscosities typically exhibit poor fuel economy due to the formation of a thicker oil film at the boundaries of the engine surfaces during engine operation. In contrast, fluids with relatively low HTHS viscosities may form a thinner oil film thereby providing improved fuel economy.
Base oils typically do not meet the viscosity requirements of SAE J300 without the addition of additives such as VIIs. VIIs may be used to reduce the extent to which the viscosity of lubricants changes with temperature, and are often used to formulate oils that meet the SAE J300 standard. Suitable VIIs typically include polymeric materials that may be derived from ethylene-propylene copolymers, polymethacrylates, hydrogenated styrene-butadiene copolymers, polyisobutylenes, etc.
Ethylene-propylene copolymers are often used as VIIs for engine oils. The ethylene content of such copolymers may range from 45 to 85 mole %. VIIs derived from such copolymers containing 60 mole % ethylene are commonly used and require a relatively high treat rate in oils in order to meet SAE J300 requirements. VIIs derived from such copolymers containing higher than about 65 mole % ethylene to 85 mole % ethylene generally require a lower treat rate in oils in order to meet SAE J300 requirements than those containing about 60 mole percent of ethylene due to their greater thickening power.
US 2013/0172220 A1 relates to additives for lubricating oil compositions which are the reaction products of: (a) an oil soluble ethylene-alpha olefin copolymer comprising 10 to less than 80 wt. % of ethylene and greater than 20 up to 90 wt. % of at least one C3-C28 alpha olefin. The copolymer has a number average molecular weight of from about 5,000 to 120,000 and is reacted or grafted with 0.5-5.0 weight percent of an ethylenically unsaturated acylating agent having at least one carboxylic acid or anhydride group, and reacted with (b) a hydrocarbyl substituted poly(oxyalkylene) monoamine of the formula:R1—(O—CHR2—CHR2)x-Awherein R1 is a hydrocarbyl group having from about 1 to about 35 carbon atoms; R2 and R3 are each independently hydrogen, methyl or ethyl; A is amino, —CH2-amino or N-alkyl amino having about 1-10 carbon atoms and x is an integer of from 2 to about 45.
U.S. Pat. No. 6,107,257 relates to additives for lubricating oil compositions that comprise multi-functional olefin copolymer viscosity index improvers. Maleic anhydride is reacted or grafted onto an ethylene-propylene copolymer backbone in the presence of a solvent and then the grafted copolymer is reacted with a polyamine such as an N-arylphenylene diamine in the presence of a surfactant to provide the multi-functional olefin copolymer viscosity index improver. Examples I and II exemplify highly grafted multi-functional olefin copolymers which are said to exhibit reduced boundary friction and improve fuel economy.
U.S. Pat. No. 6,528,461 relates to an oil of lubricating viscosity including a polymeric ethylene-alpha-olefin copolymer derived dispersant and a molybdenum compound. The ethylene-alpha-olefin copolymer dispersant is said to provide improved boundary friction properties. Examples 2A-2D employ a dispersant made by grafting maleic anhydride onto an ethylene-propylene copolymer and subsequently reacting the grafted copolymer with N-phenyl-1,4-phenylenediamine (NPPDA).
U.S. Pat. No. 8,093,189 relates to lubricating oil compositions that contain effective amounts of certain olefin copolymer dispersant viscosity index improvers that inhibit coolant-induced oil filter plugging in heavy-duty diesel engines. Example 1 of the patent, discloses a lubricating oil containing an ethylene-propylene copolymer reacted or grafted with maleic anhydride and subsequently reacted with N-phenyl-1,4-phenylenediamine.
There remains a need to provide alternative or improved engine oil compositions that meet the SAE J300 standards and pass the OM646LA engine wear test, while also providing improved fuel economy. The present invention provides engine oil compositions including grafted, multi-functional olefin copolymers that pass the OM646LA engine wear test and can provide one or more of improved wear protection, improved fuel economy, as well as acceptable soot handling, and/or engine cleanliness.